Key points:
Index Terms: 4544 Internal and inertial waves, 4562 Topographic/bathymetric interactions, 4568 Turbulence, diffusion, and mixing processes, 4223 Descriptive and regional oceanography 4262 Ocean observing systems
Keywords: Deep Argo; Deep Ocean; Vertical Velocity
Abstract Serendipitous measurements of deep internal wave signatures are evident in variations in the descent rates of certain Deep Argo floats (Deep SOLO models), which oscillate around a slow decrease with increasing pressure (and density). Averaged from 1000 dbar to the seafloor (using 10070 profiles that extend to at least 3000 dbar, and sometimes as deep as 6000 dbar) the mean of vertical velocity variances corresponds to a sinusoidal wave amplitude of about 0.007 dbar s-1. The distribution of variances is skewed towards larger values. They also exhibit notable regional variations among and within some deep ocean basins, with generally larger variances in regions of rougher topography or stronger deep currents. Dominant vertical wavelengths estimated from Morlet wavelet transform power spectra range from 393 to 1572 dbar, most frequently 786 and 935 dbar. Vertical wavelengths are weakly anticorrelated with bathymetric roughness, expectedly since shorter wavelengths should be found near generation regions.
Plain Language Summary Ocean density increases with increasing depth, supporting internal waves below the ocean surface. These internal waves are generated near the surface by unsteady wind forcing such as passing storms and near the bottom by interactions of currents (including tidal) with rough topography. They can carry energy for long distances in both the vertical and the horizontal. When they break, they play important roles in mixing temperature, salinity, and other water properties. Deep Argo is an observing system designed to measure temperature and salinity profiles from the surface to the bottom of the ocean. One model of deep Argo float serendipitously observes internal wave signals as perturbations in its descent rate, which it records primarily for navigation purposes, from the surface to the ocean floor. These observations reveal patterns in the magnitudes of these internal wave signals, with stronger internal wave activity near rough topography such as continental rises and mid-ocean ridges and lower levels over smoother abyssal plains. Also, regions with strong deep flows, such as the Samoan Passage through which bottom water is funneled into the North Pacific, or the region south of the Campbell Plateau through which the Antarctic Circumpolar Current flows, exhibit stronger deep internal wave signatures.